The present invention relates to a method and an arrangement which are used in mechanical mine clearers of the rotary cultivator type and which are intended to limit the damage to the mine clearer when the latter has come across a large mine and caused it to detonate.
Mechanical mine clearers of the rotary cultivator type are a relatively new type of mine clearer and, provided the soil is suitable for mechanical mine clearance, are able, within a short period of time, to clear considerably larger areas than is possible using other currently known clearance methods. The mechanical mine clearer clears all the mines located within its operating range by digging the soil down to a sufficient depth to reach all the mines buried in the soil, and which mines, together with the mines lying loose on the ground surface, it either tears up into smaller non-dangerous parts or causes to detonate.
Mechanical mine clearance can be carried out on all open terrain where the soil can be worked with powerful earth-working equipment, such as a plough and rotary cultivator.
Mechanical mine clearers are expected in particular to gain wide application for mine clearance on looser types of soil and non-permanently covered roadways, especially after a military conflict has ceased. There is a considerable need for this type of mine clearance today in a number of developing countries. One of the problems with the anti-personnel and anti-tank mines which have become so widely used during the twentieth century is that these mines, despite many of them being of a relatively simple construction, have nevertheless had a very long service life and can therefore be extremely dangerous even several decades after being buried. They have also been inexpensive and have therefore been used in large quantities often as weapons of terror against civilian populations in conflict areas.
What makes the mechanical mine clearer especially suited to mine clearance once a conflict has ended is that, if it is correctly constructed, it leaves behind what is in principle guaranteed to be a mine-free area, something which is not so important during a military conflict since the main objective in the latter case is to quickly achieve a mine-free corridor through which one can advance.
Even though the mechanical mine clearer is constructed so as to tear up the mines into non-dangerous parts, as far as possible without these parts detonating, one needs to take into calculation the possibility of a large number of mines detonating in or under the mine clearance equipment. This is therefore normally designed so as to withstand the mine detonations from the smaller and generally more commonly encountered anti-personnel mines, whereas in principle it is practically impossible to manufacture mine clearance equipment which fully withstands a detonation, in its immediate vicinity, of one of the larger types of anti-tank mines, which can contain anything up to 12 kg or more of high-energy explosive.
In order as far as possible to minimize the length of time for which the mechanical mine clearer is out of service after it has been exposed to a large mine detonation of this kind, the mine clearance equipment itself is designed to be easily exchangeable. A precondition for it to be sufficiently easy to replace a damaged mine clearance tool is of course that no damage has been sustained by the tool""s suspension or drive unit or by the actual motor vehicle itself.
The present invention now has the object of making available a method and an arrangement which, in the case of mechanical mine clearers of the rotary cultivator type, limit the damage sustained by the mine clearer, in the event of large mine detonations in or under the actual mine clearance tool, to the tool itself. This limitation of the damage is achieved in the first instance by the fact that the mine clearance tool, when acted upon by a large mine detonation, is allowed, by virtue of the construction of the mine clearer, to move away from the detonation site, which in reality means that the tool moves upwards, i.e. is lifted away from the detonation site. This movement is initially damped by dampers of special design also mounted between the tool""s suspension and the mine clearance vehicle.
If the detonation acting upon the mine clearance tool is so powerful that the dampers are not fully able to absorb and damp the movement of the tool relative to the rest of the mine clearance vehicle, then, according to the invention, the movement of the tool will be able to continue as a lift and tilt function which will include both the tool and its suspension in the mine clearance vehicle, and the latter""s entire engine unit. This function thus entails that the mine clearance tool and the engine together form a rigid unit which is tilted upwards and away from the detonation site about an axis of rotation arranged transverse to the actual direction of movement and fixed in the chassis of the mine clearance vehicle, which axis of rotation is positioned in such a way that more than half of the engine weight loads the tool under normal circumstances.
The possibility of in this way using large parts of the weight of the tool and engine to absorb, by means of a pivoting movement, as much as possible of the energy which the detonation has fed to the system is described in Swedish Patent Application 9702282-6.
This method makes it possible to absorb large amounts of energy by virtue of the fact that it can provide a large lifting distance for a large weight. In order for a mine clearer of the rotary cultivator type to be able to function, a powerful engine is required which is therefore large and heavy, and at the same time the cutting equipment has to be made extremely powerful and, therefore, heavy.
In the case of large anti-tank mines, or if two anti-tank mines were to detonate simultaneously in the equipment, the effect on the mine clearance tool would be so powerful that both the dampers and the above-described upward pivoting function would drop down before the full detonation energy had been consumed. In order to prevent damage to the drive function of the mine clearance tool and its suspension, the mine clearance tool according to the invention has been further designed in a special way and has been provided with specifically constructed deformation zones at the its ends. The purpose of these deformation zones is to permit a total deformation of the mine clearance tool itself, which therefore has also been made easily exchangeable, with less damage to the tools"" drive function connected to the engine and the tool""s suspension.
The mine clearance tool which is thus designed to function according to the rotary cultivator principle has the form of a central cylindrical roller provided with a large number of toothed roller discs arranged concentrically along its length, where each tooth is additionally preferably provided with an easily exchangeable hard-metal tip which is able to tear up mines and crush stones. This cylinder-shaped roller, provided with discs and teeth, is in turn rotatably mounted in a frame provided for this purpose on the mine clearance vehicle, at one end of which frame the roller communicates with the drive function which, when it is running, drives the cylinder-shaped tool, with its large number of toothed cutting discs, in rotation.
The cutting tool which forms part of the invention is now designed as a double tubular roller comprising two concentrically disposed roller tubes, of which the inner central tube bears the axle journals necessary for the bearing of the tool, while the previously mentioned toothed cutting discs are welded onto the outer tube which thus passes centrally through these. The outer tube is joined to the inner tube via end-plates which have central openings for the axle journals of the inner tube and, arranged concentrically outside these, deformation zones which, in the event of extreme stresses on the outer tube, permit a displacement of the outer tube relative to the inner tube, away from its original concentric position, without the inner tube and its bearing being affected. The deformation zones in the end-plates have been produced by forming a large number of through-holes which are arranged concentrically around the axle journal opening and which are designed in such a way that weakly S-shaped spokes have been formed between them.
The idea behind this construction is that before the stress distributed via the end-plates of the outer tube to the inner tube""s axle journals becomes so great that there is a risk of the axle journals and bearings being damaged, these end-plates of the outer tube will be deformed away from the stress point (detonation point of a detonating mine) by means of the fact that the weakly S-shaped spokes on the stress side of the axle journals are pressed together to form a more distinct S-shape while the spokes on the side away from the detonation straighten out. The result of this is that the outer roller tube is displaced away from a position concentric to the inner tube without the inner tube and its roller journals being affected, i.e. the tool is deformed and destroyed without the stresses on its bearings exceeding permitted limits.